This investigation is a case study of how a higher organism controls a simple development expression pattern. The genes to be studied are the pair of closely spaced and divergently transcribed yolk protein genes of Drosophila melanogaster. These genes have an expression pattern that is highly differentiated with respect to development of the organism and, though fairly simple, has several specificities: tissue, sex, timing within the lifetime of a cell, and hormonal response. The first objective of the project is to identify components of the mechanism by a combination of: 1) experiments which use in vitro mutagenesis and germ line transformation to identify sequences that are necessary and/or sufficient for aspects of the normal expression pattern; and 2) experiments which use DNA binding assays and cell free- transcription to identify and characterize proteins and DNA sequences which influence the yp expression pattern. The second objective is to examine interactions between identified DNA components. This will be done by manipulating component number, arrangement, and kind and then testing the consequences by germ line transformation, cell free transcription, and physical studies of protein-DNA interactions. The third objective is to determine the developmental specificities of cis-acting DNA elements which control a gene that acts in trans to determine one aspect of the yp1-2 transcription pattern.